1. Field of the Invention
The present invention relates to a heat protective lining for an afterburner duct or transition duct in a turbojet aero-engine.
Most supersonic turbojet engines are equipped with an afterburner arrangement. This is in the form of a duct which is situated between the turbine and the nozzle and to which fuel pipes supply additional fuel to complete the combustion of the hydrocarbons not burnt in the combustion chamber, thereby raising the temperature of the exhaust gases. The supply of fuel is considerable and high temperatures are reached of the order of 2100.degree. K mean exhaust temperature), and locally these temperatures may reach 2200.degree. K.
For turbojet engines fitted with axisymmetrical nozzles the duct is cylindrical in shape, and is connected upstream to the downstream collar of the exhaust housing, and downstream directly to the upstream ring of the nozzle. When the turbojet engine is equipped with a bidimensional nozzle, the afterburner duct is connected downstream to a transition duct which effects the change from a circular section to a rectangular or square section.
In view of the temperatures prevailing in the said ducts, it is essential to protect them by means of a heat protective lining. This lining is held spaced from the inner wall of the duct and coaxially with it by sliding ties. A flow of cooling air, which may be from the secondary air in the case of a bypass engine, passes between the inner wall of the duct and the outer wall of the lining.
2. Summary of the Prior Art
French Patent 1 458 204 describes a protective lining made in the form of a unitary structure having a corrugated wall. It is connected to the duct by fixed points and sliding points enabling it to expand during operation, longitudinal expansion being accommodated by the sliding points and radial expansion by deformation of the corrugations.
French Patent 2 574 859 discloses a protective lining having various cooling means. One part has a double wall cooled by impact and convection, whereas the downstream part has folds for the formation of a cooling film by internal convection. As in the Previous case, this device has the drawback that it is a one-piece unit.
In the neighbouring, but different, field of the manufacture of burners for the combustion chambers of turbojet engines, double-wall combustion chamber structures are also known, the structural outer wall bearing inner panels constituting the hot wall, the said panels being arranged in the form of overlapping tiles. U.S. Pat. No. 4,614,082, French Patent 2 567 250, British Patent 2 087 065, and U.S. Pat. No. 4,773,227 disclose examples of this arrangement.